An infrared lens using zinc sulfide as lens material is described in Patent Document 1.
Patent Document 1: Japanese Unexamined Patent Application it can not be said that an MTF (Modulation Transfer Function) obtainable from the exemplary configuration disclosed in the Patent Document 1 is sufficient, and there is a problem of poor imaging performance.
Besides, there is a concern of increasing distortion in a wide angle region (for example, in the region where a view angle is 20° or more).
Since the infrared lens described in Patent Document 1 is produced by a cutting process, there is also a problem of high processing cost.
Therefore, the invention has been made to solve the aforementioned problems, and its object is to provide a low-cost infrared lens that is suitable for a night vision requiring bright images and high imaging performance and the related technologies thereof.